Systemic Sclerosis (SSc) is a systemic inflammatory autoimmune disease characterized by progressive fibrosis of skin and multiple internal organs and severe alterations in the microvasculature. SSc has the highest case-specific mortality among the systemic autoimmune diseases and currently, there is no effective disease-modifying therapy for SSc. Therefore, there is an urgent unmet need to develop effective therapeutic approaches for the disease. Although the detailed mechanisms responsible for the progressive fibroproliferative process in SSc have not been fully elucidated recent studies, including some from our laboratories, have identified novel molecular pathways that may participate in this complex process. Recent studies have shown that SOX9, a chondrocyte-specific transcription factor, is unexpectedly involved in various fibrotic diseases including keloids and liver fibrosis. In our Preliminary Results we found that normal human dermal fibroblasts constitutively express phoshorylated Ser181 SOX9 (pSOX9), that pSOX9 levels are increased in SSc fibroblasts, and that TGF-? causes a potent stimulation of pSOX9 levels. Therefore, the overall goal of this application is to explore the role of pSOX9 in the generation of activated myofibroblasts, the cells ultimately responsible for the severe fibroproliferative process in SSc, and to examine the molecular mechanisms involved. The overarching objective of this proposal will be to: Demonstrate the profibrotic role of pSOX9 and to identify the molecular targets of pSOX9 involved in the fibrotic process. The following Specific Aims will be pursued: Specific Aim 1: Study the effects of specific inhibition of phosphorylation of SOX9 on the activated profibrotic phenotype of SSc dermal fibroblasts in vitro. Specific Aim 2: Identification of profibrotic genes displaying changes in their expression caused by the induced phosphorylation of SOX9 in normal human dermal fibroblasts employing adenoviral and lentiviral transduction of SOX9-specific kinases. Specific Aim 3: Confirm and validate the profibrotic effects of pSOX9 in vivo employing a novel strain of CRISPR-Cas9 genetically modified mice that lack the S181 phosphorylation site in SOX9 following their intercrossing with mice displaying a severe fibrotic phenotype induced by constitutively activated TGF-? signaling pathway.